The present invention relates to a lip sealing ring, particularly a valve stem seal for a poppet valve in an internal-combustion engine, the seal having a body member made of an elastic material and having, preferably, a spring-tensioned sealing lip ring and a cylindrical reinforcing ring of metal or another material. The reinforcing ring includes an attachment point for receiving an installation punch.
The fastening of valve stem rings, with or without spring-tensioned sealing lip rings, on valve stem guides is effected by means of clamps, springs, or reinforcing rings or cylinders made of metal or another hard substance which are molded or bonded into the elastic valve stem seal body. During installation, the sealing member is pressed onto the valve stem guide with the aid of a cylindrical installation punch. In order for the installation punch to be able to grip the sealing ring, the reinforcing cylinder is provided with radially outwardly extending projections which serve as installation aids.
Valve stem seals are known which are equipped with holding and installation flanges at their reinforcing cylinders. According to British Patent Specification No. 1,181,388, for example, it is known to bend the upper portion of the reinforcing cylinder radially inwardly in the region between the lower portion of the reinforcing cylinder and sealing lip member so that the resulting shoulder is the attachment point for the installation punch. According to MTZ Motortechnische Zeitschrift [Automotive Magazine] 36 (1975) No. 12, pages 326-9, valve stem seals are known in which a reinforcing cylinder is molded or bonded into the valve stem seal elastic body member and forms a type of installation collar that is bent radially outwardly in the region between the lip member and the lower region of the valve stem seal elastic body member.
The drawbacks of valve stem seals with radially outwardly projecting installation aids are that they occupy relatively large amounts of space so that such valve stem seals cannot be used, for example, in engines having two valve springs where the radial space is rather limited. In addition, in special situations where the valve has already been inserted in the guide before the valve stem seal is pressed on the valve stem, the design of the installation punch is limited. Moreover, due to their method of manufacture, the bent portions have a relatively large drawing radius and the reinforcing rings are cut such that they have a relatively wide tolerance at their outer diameter. To bridge such tolerances, the outer jacket faces of such rings must be coated with elastomers. In addition, in valve stem seals having radially inwardly or outwardly bent reinforcing rings, there exists the danger that, in the region between the sealing lip member and the reinforcing cylinder, the relatively high specific a real pressure which occurs during installation will damage the bond between the metal reinforcing ring and the valve stem elastic body member so that the entire seal may fail.